Current-limiting polyphase fuse

ABSTRACT

An electric fuse has a substantially prismatic housing or casing formed by a pair of complementary hood-shaped half-shells. An Lshaped terminal bar is affixed to each of the half-shells. Each terminal bar includes an external portion and an internal portion. The internal portions of the terminal bars extend in opposite directions each into one of said pair of half-shells and are conductively interconnected by fusible elements extending from one of the pair of half-shells into the other of the pair of half-shells.

United States Patent n 1 Jacobs, Jr.

[ 1 Jan. 23, 1973 [54] CURRENT-LIMITING POLYPHASE FUSE [75] Inventor: Philip C. Jacobs, Jr., Newtonville,

Mass.

[73] Assignee: The Chase-Shawmont Newburyport, Mass.

[22] Filed: Nov. 3, 1971 [21] Appl.No.: 195,405

Company,

[52] US. Cl. ..337/161, 337/231, 337/246, 337/252 [51] Int. Cl. ..II0lh 85/12 [58] Field of Search ..337/l58, 159, 161, 228, 229, 337/231, 232, 233, 234, 235, 236, 237, 244,

[56] References Cited UNITED STATES PATENTS 3,281,555 Fister ..337/293 X 1,377,398 5/1921 Conrad .L ..337/246 FOREIGN PATENTS OR APPLICATIONS 7,039 1902 Great Britain ..337/231 Primary Examiner-Bernard A. Gilheany Assistant ExaminerF. E. Bell Attorney-Erwin Salzer [5 7] ABSTRACT An electric fuse has a substantially prismatic housing or casing formed by a pair of complementary hoodshaped half-shells. An L-shaped terminal bar is affixed to each of the half-shells. Each terminal bar includes an external portion and an internal portion. The internal portions of the terminal bars extend in opposite directions each into one of said pair of half-shells and are conductively interconnected by fusible elements extending from one of the pair of half-shells into the other of the pair of half-shells.

6 Claims, 5 Drawing Figures CURRENT-LIMITING POLYPHASE FUSE BACKGROUND OF THE INVENTION U.S. Pat. No. 2,837,614 to A.J.Fister, June 3, 1958 for PROTECTORS FOR ELECTRIC CIRCUITS and US. Pat. No. 3,593,25l to James C. Wilson, July 13, 1971 for FUSE DEVICE disclose so-called polyphase fuses which require special insulating spacers between the terminal bars thereof. The presence of such spacers increases the cost of production and reduces the space 1 available for fusible conductor means and for pulverulent arc-quenching filler.

The patent applications of Frederick J. Kozacka filed Dec. 8, I970 Ser. No. 96,l 10 for COMPACT POLYPI-IASE FUSE, now U.S Pat. No. 3,67l,1l; issued 6/20/71, of Kenneth W. Swain et al, filed Oct. 28, 1971 Ser. No. 193,596 for POLYPI-IASE FUSE WITH BLOWN FUSE INDICATOR and of Richard Belcher et al, filed Aug. 24, 1971 Ser. No. 174,455 for ELEC- TRIC LOW-VOLTAGE FUSE disclose polyphase fuses which have no and do not require any special insulating spacers between the terminal bars thereof. The present invention relates to a fuse structure different from those disclosed in the above referred-to copending patent applications and not requiring special insulating spacers between the terminal bars The novel structure according to the present invention is more desirable in certain instances than the structures disclosed in the aforementioned copending patent applications. It is predicted on the use of complementary half-shells for forming the housing, or casing, of the fuse structure. These half-shells may be identical, if desired, thus limiting the cost of tooling.

SUMMARY OF THE INVENTION Fuses according to the present invention include a housing formed by a pair of complementary half-shells of electric insulating material having juxtaposed edges and jointly defining a pair of complementary cavities. Such fuses further include a pair of substantially L- shaped terminal bars each having an external portion projecting away from said housing and each having an internal portion. Said internal portion of each of said pair of terminal bars projects in opposite directions into one of said pair of complementary cavities and is affixed to one of said pair of half-shells. Fusible means conductively interconnect said internal portion of each of said pair of terminal bars and extend from one of said pair of complementary cavities into the other of said pair of complementary cavities. Said fusible means include ribbon fuse link means having one end connected to a point of said internal portion of one of said pair of terminal bars relatively remote from said external portion thereof and having another end connected to a point of said internal portion of the other of said pair of terminal bars relatively close to said external portion thereof. Said fusible means further include ribbon fuse link means having one end connected to a point of said internal portion of said one of said pair of terminal bars relatively close to said external portion thereof and having another end connected to a point of said internal portion of said other of said pair of terminal bars relatively remote from said external portion thereof. There is a pulverulent arc-quenching filler inside of each of said pair of complementary cavities embedding the fuse link means which are arranged therein.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an isometric view of a fuse embodying the present invention;

FIG. 2 is a vertical section of the structure of FIG. 1, in substance along 2-2 of FIG. 1;

FIG. 3 is an isometric view of another fuse embodying the present invention;

FIG. 4 is a vertical section of the structure of FIG. 3

0 in substance along 44 of FIG. 3; and

FIG. 5 is a top-plan view of a polyphase version of the structure substantially as shown in FIGS. 1 and 2.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, housing la,lb is formed by a pair of complementary half-shells 1a and 1b of electric insulating material having juxtaposed engaging edges 2a and 2b. Half-shells 1a and lb jointly define a pair of complementary cavities 3a and 3b. Reference characters 4a,4b and 5a,5b have been applied to indicate a pair of substantially L-shaped terminal bars. Each terminal bar includes an external portion 4a and 5a, respectively, projecting away from housing la,lb. Each of said pair of terminal bars 4a,4b and 5a,5b further includes an internal portion 4b and 5b projecting in opposite directions into one of cavities 3a,3b. The internal portion 4b of terminal bar 4a,4b is affixed to half-shell la, e.g. cemented to the latter. This may readily be achieved by means of an epoxy resin cement. The internal portion 5b of terminal bar 5a,5b is affixed to half-shell 1b. Ribbon fuse link means 6 conductively interconnect the internal portions 4b,5b of the pair of terminal bars 4a,4b and 5a,5b and extend from one of the pair of complementary cavities 3a into the other of said pair of cavities 3b. This imparts a relatively great length to fuse link means 6 tending to yield a relatively high arc-voltage incident to blowing of the fuse by major fault currents. Cavities 3a,3b are filled with a pulverulent arc-quenching filler 7 (only indicated in part) embedding fuse link means 6.

In the structure of FIGS. 1 and 2 the half-shells la,lb have a different geometry, one of them being provided with a hollow projection 8 for receiving a spring-biased blown fuse indicator 9 and the other being provided with, a filling aperture 10 for arc-quenching filler 7 which aperture is closed by a plug 11 upon completion of the assembly. of the fuse structure. The blown fuse indicator 9 is normally held in position by a V-shaped restraining wire 12 whose ends are affixed by means of screws 13 to the external portions 4a,5a of terminal bars 4a,4b and 5a,5b.

In the structure of FIGS. 3 and 4 both half-shells la,1b' are congruent and engage along edges la',1b'.

In all embodiments of the invention shown half-shells la,lb and la,1b, respectively, are joined together by studs 17,17 and 17'', respectively.

In the structure of FIGS. 1 and 2 the external portions 4a,4b of terminal bars 4a,4b and 5a,5b are arranged substantially in the plane defined by the juxtaposed edges 2a,2b of half-shells la,lb.

In FIGS. 3 and 4 the same reference characters have been applied as in FIGS. 1 and 2 to indicate like parts, except that a prime has been added to all reference characters appearing in FIGS. 3 and 4.

According to FIGS. 3 and 4 juxtaposed walls l4a',l4 b of half-shells la',1b' are provided with one of a pair of perforations la',15b'. The external portions 4a,5a of each pair of L-shaped terminal bars 4a',4b and 5a',5 b project through perforations 15a',15b' from the inside of the housing formed by half-shells la',lb to the outside thereof. The plane generally defined by the juxtaposed edges 2a,2b' of half-shells la',lb is positioned substantially at right angles to the plane defined by external portions 4a',5a of terminal bars 4a,4b' and 5a,5b. Each half-shell la',lb has a semi-cylindrical aperture a and 10b, respectively, jointly defining a cylindrical passageway closed by a plug 11. The complementary cavities 3a ,3b' formed by half-shells la',lb are filled with pulverulent arc-quenching filler 7'. The internal portions 4b,5b of terminal bars 4a',4b' and Sa',5b' are conductively interconnected by ribbon fuse links 6 of silver submersed in arc-quenching filler 7 and extending from cavity 3a into cavity 3b across the plane defined by shell edges 2a,2b'. Each hood-shaped half-shell la',lb is provided with a hollow projection 8' in the form of one half of a solid of revolution. Projections 8 are complementary and form a housing for blown fuse indicator 9'. The axially inner end of blown fuse indicator housing 8 has a perforation for the passage of restraining wire 12' whose ends are affixed by means of screws 13' to the external portions 4a',5a of terminal bars 4a',4b' and 5a,5b.

The structure shown in FIG. 5 is substantially the same as that shown in FIGS. 1 and 2 but involves three integral phase units rather than one single phase unit. FIG. 5 shows below three external portions 4a" of L- shaped terminal bars and above three external portions 5a" of three L-shaped terminal bars. The upper halfshell la" abuts against a lower half-shell (not shown), both being tied together by studs 17". Both half-shells form jointly three separate compartments of which each has a filling hole 10" closed by a plug 11".

It is necessary or desirable to seal half-shells la,lb and la',lb along the edges 2a,2b (FIGS. 1 and 2) and 2a,2b (FIGS. 3 and 4), respectively. It is further necessary or desirable to seal the points where terminal bars 4a,4b and 5a,5b (FIGS. 1 and 2) and 4a,4b and 5a,5b' (FIGS. 3 and 4) project from the inside to the outside of the casing 1a,1b and la',lb. This can best be achieved without use of gaskets by the application of self-curing silicone rubber in paste-form.

It will be noted that half-shells la,lb and la',lb are the only means for positioning and spacing terminal bars 4a,4b; 5a,5b and 4a,4b 5a,5b". The complementary cavities 3a,3b;3a,3b are unencumbered by spacing posts of insulating material extending between the internal portions 4b,5b;4b,5b' of terminal bars 4a,4b; 5a,5b; 4a,4b, 5a,5b'.

It will be apparent from FIGS. 2 and 3 that the fuse link 6,6 arranged on the highest level has one end (left) connected to a point of the internal portion 4b,4bof terminal bar 4a,4b;4a,4b' relatively remote from the external portion 4a,4a' thereof. The other end (right) of fuse link 6,6 arranged at the highest level is connected to a point of the internal portion 5b,5b' of terminal bar 5a,5b;5a,5b which is relatively close to said external portion 5a,5a' thereof. Considering now the ribbon fuse link 6,6 arranged on the lowest level, one end (left) thereof is connected to a point of the internal portion 4b,4b of terminal bar 4a,4b;4a',4b relatively close to the external portion 4a,4a thereof. The

other end of the fuse link 6,6 arranged at the lowest level is connected to a point of the internal portion 5b,5bof terminal bar 5a,5b;5a',5b' which is relatively remote from the external portion 5a, 50' thereof. As a 5 result of this geometry, the current path from portion 4a to portion 5a is of equal length through either of the two fuse links at the highest level and the lowest level which have been considered above, and the same is also true in regard to the two intermediate ribbon fuse links 6,6. Equality of the length of the current paths of all ribbon fuse links 6,6 results in equality of the ohmic resistance thereof.

The assembly of the structure of FIGS. 1 and 2 can be effected as follows: The right ends of ribbon fuse links 6 are inserted into grooves 19b provided in the end 5b of terminal bar 5a,5b and connected with it by solder joints. Thereupon terminal bar 5a,5b with the fuse links 6 affixed to it may be inserted into and secured to half-shell lb. Now the left ends of fuse links 6 are inserted into the grooves 19a in terminal bar 4a,4b and connected to it by solder joints. Then terminal bar 4a,4b is inserted into, and affixed to, halfshell 1a which is positioned to engage with its edge 2a the edge 2b of lower half-shell 1b. Inserting terminal bar 4a,4b into half-shell la and affixing the former to the latter is a single step operation if the terminal bar 4a,4b is cemented to half-shell 1a. The step of cementing terminal bars 4a,4b; 5a,5b to half-shells 1a,lb is greatly facilitated if half-shells 1a,lb are provided with grooves into which the internal portions 4b,5b of terminal bars 40,4 b; 5a,5b can be fitted readily. Such grooves have been indicated in FIG. 2 by reference characters 18a,18b.

The structure of FIGS. 3 and 4 can be assembled in substantially the same way as that of FIGS. 1 and 2.

The fuses disclosed above are intended to back-up other switching equipment such as, for instance, molded case circuit breakers or motor starters. Major fault currents result in fusion of fusible elements 6 or 6' in periods of time less than a quarter cycle of a current wave. Thus an arc-voltage is formed between terminal bars 4a,4b;5a,5b or 4a,4b'; 5a,5b, respectively. This causes fusion of restraining wires 7 or 7', respectively, and activation of blown fuse indicators 9 or 9', respectively.

I claim as my invention.

1. An electric fuse including a. a housing formed by a pair of complementary halfshells of electric insulating material having juxtaposed engaging edges and jointly defining a pair of complementary cavities;

. a pair of substantially L-shaped terminal bars each including an external portion projecting away from said housing and each including an internal portion, said internal portion of each of said pair of terminal bars projecting in opposite directions into one of said pair of complementary cavities and being affixed to one of said pair of half-shells;

. fusible means conductively interconnecting said internal portion of each of said pair of terminal bars and extending from one of said pair of complementary cavities across the plane defined by said juxtaposed engaging edges into the other of said pair of complementary cavities, said fusible means including ribbon fuse link means having one end connected to a point of said internal portion of one of said pair of terminal bars relatively remote from said external portion thereof and having another end connected to a point of said internal portion of the other of said pair of terminal bars relatively close to said external portion thereof, and said fusible means further including ribbon fuse link means having one end connected to a point of said internal portion of said one of said pair of terminal bars relatively close to said external portion thereof and having another end connected to a point of said internal portion of said other of said pair of terminal bars relatively remote from said external portion thereof; and

. a pulverulent arc-quenching filler inside of each of said pair of complementary cavities embedding said fusible means.

2. An electric fuse as specified in claim 1 wherein said complementary half-shells are substantially congruent.

3. An electric fuse as specified in claim 1 wherein said pair of half-shells is the only means positioning and spacing said pair of terminal bars, said pair of complementary cavities being unencumbered by spacing posts of insulating material extending between said internal portion of each of said pair of terminal bars.

4. An electric fuse as specified in claim 1 wherein said external portion of each of said pair of terminal bars is arranged substantially in a plane defined by said juxtaposed edges of said pair of half-shells.

5. An electric fuse as specified in claim 1 wherein juxtaposed walls of each of said pair of half-shells are provided with one of a pair of perforations, said external portion of each of said pair of terminal bars projecting through one of said pair of perforations from the inside of said housing to the outside thereof, and wherein the plane generally defined by said juxtaposed edges of said pair of half-shells is positioned substantially at right angles to the plane defined by said external portion of each of said pair of terminal bars.

6. An electric low-voltage fuse including a. a pair of complementary substantially hoodshaped half-shells of electric insulating material arranged to abut against each other with juxtaposed edges thereof and jointly forming a substantially prismatic casing; b. a pulverulent arc-quenching filler inside said casing; a pair of substantially L-shaped terminal bars each having an external portion projecting away from said casing and each having an internal portion at right angles to said external portion, said internal portion of each of said pair of terminal bars projecting in opposite directions away from said external portion thereof into one of said pair of halfshells; and d. fusible means submersed in said pulverulent arcquenching filler projecting substantially transversely across the plane generally defined by said juxtaposed edges of said pair of half-shells and conductively interconnecting said internal portion of each of said pair of terminal bars, said fusible means including ribbon fuse link means having one end connected to a point of said internal portion of one of said pair of terminal bars relatively remote from said external portion thereof an having another end connected to a point of said internal portion of the other of said pair of terminal bars relatively close to said external portion thereof, and said fusible means further including ribbon fuse link means having one end connected to a point of said internal portion of said one of said pair of terminal bars relatively close to said external portion thereof and having another end connected to a point of said internal portion of said other of said pair of terminal bars relatively remote from said external portion thereof. 

1. An electric fuse including a. a housing formed by a pair of complementary half-shells of electric insulating material having juxtaposed engaging edges and jointly defining a pair of complementary cavities; b. a pair of substantially L-shaped terminal bars each including an external portioN projecting away from said housing and each including an internal portion, said internal portion of each of said pair of terminal bars projecting in opposite directions into one of said pair of complementary cavities and being affixed to one of said pair of half-shells; c. fusible means conductively interconnecting said internal portion of each of said pair of terminal bars and extending from one of said pair of complementary cavities across the plane defined by said juxtaposed engaging edges into the other of said pair of complementary cavities, said fusible means including ribbon fuse link means having one end connected to a point of said internal portion of one of said pair of terminal bars relatively remote from said external portion thereof and having another end connected to a point of said internal portion of the other of said pair of terminal bars relatively close to said external portion thereof, and said fusible means further including ribbon fuse link means having one end connected to a point of said internal portion of said one of said pair of terminal bars relatively close to said external portion thereof and having another end connected to a point of said internal portion of said other of said pair of terminal bars relatively remote from said external portion thereof; and d. a pulverulent arc-quenching filler inside of each of said pair of complementary cavities embedding said fusible means.
 2. An electric fuse as specified in claim 1 wherein said complementary half-shells are substantially congruent.
 3. An electric fuse as specified in claim 1 wherein said pair of half-shells is the only means positioning and spacing said pair of terminal bars, said pair of complementary cavities being unencumbered by spacing posts of insulating material extending between said internal portion of each of said pair of terminal bars.
 4. An electric fuse as specified in claim 1 wherein said external portion of each of said pair of terminal bars is arranged substantially in a plane defined by said juxtaposed edges of said pair of half-shells.
 5. An electric fuse as specified in claim 1 wherein juxtaposed walls of each of said pair of half-shells are provided with one of a pair of perforations, said external portion of each of said pair of terminal bars projecting through one of said pair of perforations from the inside of said housing to the outside thereof, and wherein the plane generally defined by said juxtaposed edges of said pair of half-shells is positioned substantially at right angles to the plane defined by said external portion of each of said pair of terminal bars.
 6. An electric low-voltage fuse including a. a pair of complementary substantially hood-shaped half-shells of electric insulating material arranged to abut against each other with juxtaposed edges thereof and jointly forming a substantially prismatic casing; b. a pulverulent arc-quenching filler inside said casing; c. a pair of substantially L-shaped terminal bars each having an external portion projecting away from said casing and each having an internal portion at right angles to said external portion, said internal portion of each of said pair of terminal bars projecting in opposite directions away from said external portion thereof into one of said pair of half-shells; and d. fusible means submersed in said pulverulent arc-quenching filler projecting substantially transversely across the plane generally defined by said juxtaposed edges of said pair of half-shells and conductively interconnecting said internal portion of each of said pair of terminal bars, said fusible means including ribbon fuse link means having one end connected to a point of said internal portion of one of said pair of terminal bars relatively remote from said external portion thereof and having another end connected to a point of said internal portion of the other of said pair of terminal bars relatively close to said external portion thereof, and said fusible means further including ribbon fuse link mEans having one end connected to a point of said internal portion of said one of said pair of terminal bars relatively close to said external portion thereof and having another end connected to a point of said internal portion of said other of said pair of terminal bars relatively remote from said external portion thereof. 